Image sensor, imaging device and imaging method

ABSTRACT

An image sensor includes imaging pixels that convert an image formed via an optical system to image signals and a first focus detection pixel group and a second focus detection pixel group respectively made up with an array of first focus detection pixels and an array of second focus detection pixels, with the first focus detection pixels and the second focus detection pixels used to receive an image light flux via the optical system to detect a focus adjustment state at the optical system through a pupil division-type method. An image detection pitch of the first focus detection pixel group and an image detection pitch of the second focus detection pixel group are different from each other.

INCORPORATION BY REFERENCE

The disclosure of the following priority application is hereinincorporated by reference:

Japanese Patent Application No. 2006-104402 filed Apr. 5, 2006

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image sensor that includes aplurality of imaging pixels and a plurality of pupil division-type focusdetection pixels arrayed on a single substrate, an image sensor as aphotoelectric conversion element, an imaging device equipped with theimage sensor and the imaging method.

2. Description of the Related Art

There is an imaging device known in the related art equipped with animage sensor having imaging pixels and pupil division-type focusdetection pixels disposed together on a single substrate, which capturesan image formed on the image sensor and also detects the focusadjustment state of the image (see Japanese Laid Open Patent PublicationNo. H01-216306).

The following problems arise in the imaging device in the related artdescribed above, which detects the focus adjustment state based upon theimage shift amount between a pair of images detected through the pupildivision-type method. Namely, in order to assure highly accuratedetection of the focus adjustment state in the range around the imagefocus match position, the focus detection pixels should be disposeddensely so as to set a short (fine) image detection pitch. At the sametime, the focus detection pixels should be arrayed over a long range toenable detection of a large image shift amount between the pair ofimages when the image is greatly defocused from the focus match position(hereafter may also be referred to as large defocusing) by assuring asufficient image shift amount margin. In short, the focus detectionpixels should be disposed densely over a long row in order to assureboth highly accurate focus detection and detection of a large defocusamount.

For the image sensor to provide high quality image signals, pixelsignals at the focus detection pixel positions should be interpolatedbased upon the signals from the surrounding imaging pixels. This meansthat the likelihood of a significant interpolation error is bound to behigh when interpolating (correcting) pixel signals at positions taken upby the individual focus detection pixels, which are disposed denselyover a long range, based upon the signals from the surrounding imagingpixels.

SUMMARY OF THE INVENTION

According to the 1st aspect of the invention, an image sensor comprisesimaging pixels that convert an image formed via an optical system toimage signals, and a first focus detection pixel group and a secondfocus detection pixel group respectively made up with an array of firstfocus detection pixels and an array of second focus detection pixels,with the first focus detection pixels and the second focus detectionpixels used to receive an image light flux via the optical system todetect a focus adjustment state at the optical system through a pupildivision-type method. An image array pitch with which the image isdetected via the first focus detection pixel group and an imagedetection pitch with which the image is detected via the second focusdetection pixel group are different from each other.

In the image sensor, an array pitch at which the first focus detectionpixels may be disposed in the first focus detection pixel group and anarray pitch at which the second focus detection pixels may be disposedin the second focus detection pixel group are different from each other.

The second focus detection pixel group may range over a greater lengththan the first focus detection pixel group. An array direction of thefirst focus detection pixel group and an array direction of the secondfocus detection pixel group may match each other.

The first focus detection pixel group and the second focus detectionpixel group may be set in close proximity to each other, or may be setalong a single straight line.

The second focus detection pixel group can be disposed at an end of thefirst focus detection pixel group.

The first focus detection pixels and the second focus detection pixelsmay have sensitivity over a wider wavelength range than pixels otherthan the first focus detection pixels and the second focus detectionpixels.

The first focus detection pixels and the second focus detection pixelscan be each constituted with a micro-lens and a photoelectric conversionunit.

The photoelectric conversion unit maybe formed so as to allow the pairof areas at the exit pupil of the optical system to partially overlap.

An interval between gravitational centers of the pair of areas at theexit pupil of the optical system, which corresponds to the first focusdetection pixels, and an interval between gravitational centers of thepair of areas at the exit pupil of the optical system, which correspondsto the second focus detection pixels, maybe different from each other.

The first focus detection pixels and the second focus detection pixelsmay each detect a pair of images formed with light fluxes passingthrough a pair of areas at an exit pupil of the optical system.

According to the 2nd aspect of the invention, an image sensor comprisesan imaging pixel group made up with pixels that convert an image formedvia an optical system to image signals, formed by arraying a pluralityof pixel sets each constituted with a plurality of pixels withsensitivity to different colors, and a first focus detection pixel groupand a second focus detection pixel group respectively made up with anarray of first focus detection pixels and an array of second focusdetection pixels, with the first focus detection pixels and the secondfocus detection pixels used to receive an image light flux via theoptical system to detect a focus adjustment state at the optical systemthrough a pupil division-type method. An image detection pitch withwhich the image is detected via the second focus detection pixel groupis larger than an image detection pitch with which the image is detectedvia the first focus detection pixel group. The first focus detectionpixel group and the second focus detection pixel group are disposed atpositions corresponding to pixels sensitive to a color with lowluminosity factor in the pixel sets each constituted with a plurality ofpixels.

The pixel sets may each include a plurality of pixels sensitive to red,green and blue disposed in a Bayer array, and the first focus detectionpixel group and the second focus detection pixel group are disposed atpositions corresponding to pixels with sensitivity to blue and green ina two-dimensional array of the imaging pixels.

According to the 3^(rd) aspect of the invention, an image sensorcomprises imaging pixels that convert an image formed via an opticalsystem to image signals, and a first focus detection pixel group and asecond focus detection pixel group respectively made up with an array offirst focus detection pixels and an array of second focus detectionpixels, with the first focus detection pixels and the second focusdetection pixels used to receive an image light flux via the opticalsystem to detect a focus adjustment state at the optical system througha pupil division-type method. An image detection pitch with which theimage is detected via the second focus detection pixel group is largerthan an image detection pitch with which the image is detected via thefirst focus detection pixel group. The first focus detection pixels andthe second focus detection pixels each detect a pair of images formedwith light fluxes passing through a pair of areas at an exit pupil ofthe optical system, and an interval between gravitational centers of thepair of areas at the exit pupil of the optical system, which correspondto the second focus detection pixels, is shorter than an intervalbetween gravitational centers of the pair of areas at the exit pupil ofthe optical system, which corresponds to the first focus detectionpixels.

According to the 4th aspect of the invention, an image sensor comprisesimaging pixels that convert an image formed via an optical system toimage signals, and a first focus detection pixel group and a secondfocus detection pixel group respectively made up with an array of firstfocus detection pixels and an array of second focus detection pixels,with the first focus detection pixels and the second focus detectionpixels used to receive an image light flux via the optical system todetect a focus adjustment state at the optical system through a pupildivision-type method. An image detection pitch with which the image isdetected via the second focus detection pixel group is larger than animage detection pitch with which the image is detected via the firstfocus detection pixel group. A width over which the pair of areas at theexit pupil of the optical system, which correspond to the second focusdetection pixels, range along a direction in which pupils are setside-by-side is smaller than a width over which the pair of areas at theexit pupil of the optical system, which correspond to the first focusdetection pixels, range along the direction in which pupils are setside-by-side.

According to the 5th aspect of the invention, an image sensor comprisesimaging pixels that convert an image formed via an optical system toimage signals, and a first focus detection pixel group and a secondfocus detection pixel group respectively made up with an array of firstfocus detection pixels and an array of second focus detection pixels,with the first focus detection pixels and the second focus detectionpixels used to receive an image light flux via the optical system todetect a focus adjustment state at the optical system through a pupildivision-type method. An image detection pitch with which the image isdetected via the second focus detection pixel group is larger than animage detection pitch with which the image is detected via the firstfocus detection pixel group. The first focus detection pixels and thesecond focus detection pixels each include a photoelectric conversionunit disposed at a position further toward one side relative to a pixelcenter portion.

According to the 6th aspect of the invention, an imaging devicecomprises an image sensor that includes imaging pixels that convert animage formed via an optical system to image signals and a first focusdetection pixel group and a second focus detection pixel grouprespectively made up with an array of first focus detection pixels andan array of second focus detection pixels, with the first focusdetection pixels and the second focus detection pixels used to receivean image light flux via the optical system to detect a focus adjustmentstate at the optical system through a pupil division-type method, and afocus detection unit that detects the focus adjustment state at theoptical system based upon outputs from the first focus detection pixelgroup and the second focus detection pixel group. An image detectionpitch with which the image is detected via the first focus detectionpixel group and an image detection pitch with which the image isdetected via the second focus detection pixel group are different fromeach other.

The focus detection unit may select one of an output from the firstfocus detection pixel group and an output from the second focusdetection pixel group in correspondence to the focus adjustment state.The imaging device may further comprise a pixel output generation unitthat generates pixel outputs in correspondence to positions of the firstfocus detection pixels and the second focus detection pixels based uponoutputs from pixels surrounding the first focus detection pixels and thesecond focus detection pixels.

According to the 7th aspect of the invention, an image sensor comprisesa first focus detection pixel group made up with an array of first focusdetection pixels each equipped with a first photoelectric conversionunit at which an image light flux via an optical system is received soas to detect a focus adjustment state at the optical system through apupil division-type method based upon an output from the firstphotoelectric conversion unit, and a second focus detection pixel groupmade up with an array of second focus detection pixels each equippedwith a second photoelectric conversion unit different from the firstphotoelectric conversion unit so as to detect the focus adjustment stateat the optical system through a pupil division-type method based upon anoutput from the second photoelectric conversion unit.

An image detection pitch with which the image is detected via the secondfocus detection pixel group can be larger than an image detection pitchat which the image is detected via the first focus detection pixelgroup.

An array pitch at which the second focus detection pixels may bedisposed in the second focus detection pixel group is larger than anarray pitch at which the first focus detection pixels are disposed inthe first focus detection pixel group.

According to the 8th aspect of the invention, an imaging methodcomprises providing an image sensor that includes imaging pixels thatconvert an image formed via an optical system to image signals,providing in the image sensor a first focus detection pixel group and asecond focus detection pixel group respectively made up with an array offirst focus detection pixels and an array of second focus, detectionpixels, with the first focus detection pixels and the second focusdetection pixels used to receive an image light flux via the opticalsystem to detect a focus adjustment state at the optical system througha pupil division-type method, detecting the focus adjustment state atthe optical system based upon outputs from the first focus detectionpixel group and the second focus detection pixel group, and setting animage detection pitch with which the image is detected via the firstfocus detection pixel group and an image detection pitch with which theimage is detected via the second focus detection pixel group differentlyfrom each other.

According to the 9th aspect of the invention, an imaging methodcomprises providing an image sensor that includes an imaging pixel groupmade up with pixels that convert an image formed via an optical systemto image signals, which is formed by arraying a plurality of pixel setseach constituted with a plurality of pixels with sensitivity todifferent colors, providing in the image sensor a first focus detectionpixel group and a second focus detection pixel group respectively madeup with an array of first focus detection pixels and an array of secondfocus detection pixels, with the first focus detection pixels and thesecond focus detection pixels used to receive an image light flux viathe optical system to detect a focus adjustment state at the opticalsystem through a pupil division-type method, detecting the focusadjustment state at the optical system based upon outputs from the firstfocus detection pixel group and the second focus detection pixel group,and setting the first focus detection pixel group and the second focusdetection pixel group at the image sensor so that an image detectionpitch at which the image is detected via the second focus detectionpixel group is larger than an image detection pitch at which the imageis detected via the first focus detection pixel group, at positionscorresponding to pixels sensitive to a color with low luminosity factorin the pixel sets, each constituted with a plurality of pixels.

According to the 10th aspect of the invention, an imaging methodcomprises providing an image sensor that includes imaging pixels thatconvert an image formed via an optical system to image signals,providing in the image sensor a first focus detection pixel group and asecond focus detection pixel group respectively made up with an array offirst focus detection pixels and an array of second focus detectionpixels, with the first focus detection pixels and the second focusdetection pixels used to receive an image light flux via the opticalsystem to detect a focus adjustment state at the optical system througha pupil division-type method, detecting the focus adjustment state atthe optical system based upon outputs from the first focus detectionpixel group and the second focus detection pixel group, generated bydetecting via each of the first focus detection pixels and the secondfocus detection pixels a pair of images formed with light fluxes passingthrough a pair of areas at an exit pupil of the optical system, settingthe first focus detection pixel group and the second focus detectionpixel group at the image sensor so that an image detection pitch withwhich the image is detected via the second focus detection pixel groupis larger than an image detection pitch with which the image is detectedvia the first focus detection pixel group, and making an intervalbetween gravitational centers of the pair of areas at the exit pupil ofthe optical system, which correspond to the second focus detectionpixels shorter than an interval between gravitational centers of thepair of areas at the exit pupil of the optical system, which correspondsto the first focus detection pixels.

According to the 11th aspect of the invention, an imaging methodcomprises providing an image sensor that includes imaging pixels thatconvert an image formed via an optical system to image signals,providing in the image sensor a first focus detection pixel group and asecond focus detection pixel group respectively made up with an array offirst focus detection pixels and an array of second focus detectionpixels, with the first focus detection pixels and the second focusdetection pixels used to receive an image light flux via the opticalsystem to detect a focus adjustment state at the optical system througha pupil division-type method, detecting the focus adjustment state atthe optical system based upon outputs from the first focus detectionpixel group and the second focus detection pixel group, setting thefirst focus detection pixel group and the second focus detection pixelgroup at the image sensor so that an image detection pitch with whichthe image is detected via the second focus detection pixel group islarger than an image detection pitch with which the image is detectedvia the first focus detection pixel group, and disposing the first focusdetection pixels and the second focus detection pixels so that a widthover which the pair of areas at the exit pupil of the optical system,which correspond to the second focus detection pixels, range along adirection in which pupils are set side-by-side is smaller than a widthover which the pair of areas at the exit pupil of the optical system,which correspond to the first focus detection pixels, range along thedirection in which the pupils are set side-by-side.

According to the 12th aspect of the invention, an imaging methodcomprises providing an image sensor that includes imaging pixels thatconvert an image formed via an optical system to image signals,providing in the image sensor a first focus detection pixel group and asecond focus detection pixel group respectively made up with an array offirst focus detection pixels and an array of second focus detectionpixels, with the first focus detection pixels and the second focusdetection pixels used to receive an image light flux via the opticalsystem to detect a focus adjustment state at the optical system througha pupil division-type method, detecting a focus adjustment state at theoptical system based upon outputs from the first focus detection pixelgroup and the second focus detection pixel group, disposing the firstfocus detection pixel group and the second focus detection pixel groupat the image sensor so that an image detection pitch with which theimage is detected via the second focus detection pixel group is largerthan an image detection pitch with which the image is detected via thefirst focus detection pixel group and providing a photoelectricconversion unit disposed at a position further toward one side relativeto a pixel center portion in the first focus detection pixels and thesecond focus detection pixels.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the structure of the digital still camera in an embodimentof the present invention;

FIG. 2 shows the focus detection areas on the imaging plane set on theestimated image forming plane of the exchangeable lens;

FIG. 3 shows the arrangement of color filters disposed at the imagesensor;

FIG. 4 shows the sensitivity characteristics of the imaging pixels eachhaving a primary color filter corresponding to one of the three primarycolors R, G and B, disposed thereat;

FIG. 5 shows the relative luminosity of G filter pixels;

FIG. 6 shows an arrangement that may be adopted for complementary colorfilters;

FIG. 7 is a front view, showing in detail the structure of the imagesensor;

FIG. 8 shows an imaging pixel in an enlargement;

FIG. 9 shows a first focus detection pixel in an enlargement;

FIG. 10 shows a second focus detection pixel in an enlargement;

FIG. 11 shows the characteristics of the filters mounted at the firstfocus detection pixels and the second focus detection pixels;

FIGS. 12A and 12B show how an image formed on the image sensor issampled via the first focus detection pixels and the second focusdetection pixels;

FIG. 13 is a sectional view of an imaging pixel;

FIG. 14 is a sectional view of a first focus detection pixel or a secondfocus detection pixel;

FIG. 15 illustrates focus detection executed through the pupildivision-type method;

FIG. 16 is a front view, showing the relationship between the projectionareas (range-finding pupils) of the pair of photoelectric conversionunits in a first focus detection pixel over the exit pupil plane of theexchangeable lens;

FIG. 17 is a front view, showing the relationship between the projectionareas (range-finding pupils) of the pair of photoelectric conversionunits in a second focus detection pixel over the exit pupil plane of theexchangeable lens;

FIG. 18 shows the relationship among the defocus amount, the image shiftamount at the image sensor surface and the positions of thegravitational centers of the range-finding pupils on the exit pupil;

FIGS. 19A-19 c show the distribution of the image intensity detected byvarying the width of one of the range-finding pupils measured along thedirection in which the pupils are set side-by-side from a small settingto an intermediate setting and a large setting relative to a largedefocus amount that remains constant (relative to a constant image shiftamount);

FIG. 20 presents a flowchart of the operations executed in the digitalstill camera (imaging device) shown in FIG. 1;

FIG. 21 presents a flowchart of the image shift detection calculationprocessing (correlational algorithm);

FIGS. 22A-22C illustrate the concept of the image shift detectioncalculation processing (correlational algorithm);

FIG. 23 shows the positional arrangement adopted for the first focusdetection pixel row (AF 1-AF 5) and the surrounding imaging pixels (bluepixels B1-B6, red pixels R1-R4 and green pixels G1-G10);

FIG. 24 shows the image sensor in a variation;

FIGS. 25A and 25B show first focus detection pixels in a variation;

FIGS. 26A and 26B show first focus detection pixels in anothervariation;

FIGS. 27A and 27B show second focus detection pixels in a variation;

FIG. 28 shows the image sensor in yet another variation;

FIG. 29 shows the image sensor in yet another variation;

FIG. 30 shows the image sensor in yet another variation;

FIG. 31 shows the image sensor in yet another variation; and

FIG. 32 illustrates a pupil division-type method in conjunction withpolarization filters.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An explanation is now given on an embodiment by adopting the presentinvention in a digital still camera. It is to be toted that the presentinvention may also be effectively adopted in a compact digital camera, avideo camera, a compact camera module built into a portable telephoneand the like, as well as in a digital still camera. In addition, thepresent invention may be adopted in a camera with an integrated lens,instead of a camera with an exchangeable lens mounted at the camerabody.

FIG. 1 shows the structure of the digital still camera in theembodiment. The digital still camera 201 in the embodiment comprises anexchangeable lens unit 202 and a camera body 203. The exchangeable lensunit 202 is mounted on a mount unit 204 at the camera body 203.

The exchangeable lens unit 202 includes lenses 205-207, an aperture 208and a lens drive control device 209. It is to be noted that the lens 206is a zooming lens and that the lens 207 is a focusing lens. The lensdrive control device 209, constituted with a CPU and its peripheralcomponents, controls the drive of the focusing lens 207 and the aperture208, detects the positions of the zooming lens 206, the focusing lens207 and the aperture 208 and transmits lens information and receivescamera information by communicating with a control device in the camerabody 203.

An image sensor 211, a camera drive control device 212, a memory card213, an LCD driver 214, an LCD 215, an eyepiece lens 216 and the likeare mounted at the camera body 203. The image sensor 211, set at theestimated image forming plane (estimated focal plane) of theexchangeable lens unit 202, captures a subject image formed through theexchangeable lens unit 202 and outputs image signals. At the imagesensor 211, pixels used for imaging (hereafter simply referred to asimaging pixels) are disposed two-dimensionally, and rows of pixels usedfor focus detection (hereafter simply referred to as focus detectionpixels), instead of imaging pixels, are disposed in the two-dimensionalarray over areas corresponding to focus detection positions. It is to benoted that the image sensor 211 may be a CCD image sensor or a CMOSimage sensor.

The camera drive control device 212, constituted with a CPU and itsperipheral components, controls the drive of the image sensor 211,processes the captured image, executes focus detection and focusadjustment for the exchangeable lens unit 202, controls the aperture208, controls display operation at the LCD 215, communicates with thelens drive control device 209 and controls the overall operationalsequence in the camera. It is to be noted that the camera drive controldevice 212 communicates with the lens drive control device 209 via anelectrical contact point 217 at the mount unit 204.

The memory card 213 is an image storage device in which captured imagesare stored. The LCD 215 is used as a display unit of a liquid crystalviewfinder (EVF: electronic viewfinder). The photographer is able tovisually check a captured image displayed at the LCD 215 via theeyepiece lens 216.

The subject image formed on the image sensor 211 after passing throughthe exchangeable lens unit 202 undergoes photoelectric conversion at theimage sensor 211 and the post-photoelectric conversion output isprovided to the camera drive control device 212. The camera drivecontrol device 212 determines through arithmetic operation the defocusamount at a focus detection position based upon the outputs from thefocus detection pixels and transmits the defocus amount to the lensdrive control device 209. In addition, the camera drive control device212 provides image signals generated based upon the outputs from theimaging pixels to the LCD driver 214 so as to display the captured imageat the LCD 215 and also stores the image signals into the memory card213.

The lens drive control device 209 detects the positions of the zoominglens 206, the focusing lens 207 and the aperture 208 and obtains througharithmetic operation the lens information based upon the detectedpositions. It is to be noted that the lens information corresponding tothe detected positions may be selected from a lookup table prepared inadvance. The lens information is then provided to the camera drivecontrol device 212. In addition, the lens drive control device 209calculates a lens drive amount indicating the extent to which the lensis to be driven based upon the defocus amount received from the cameradrive control device 212, and controls the drive of the focusing lens207 based upon the lens drive amount.

FIG. 2 shows focus detection areas on an imaging plane G set on theestimated image forming plane of the exchangeable lens unit 202. Focalpoint detection areas G1˜G5 are set on the imaging plane G and the focusdetection pixels are arrayed at the image sensor 211 in correspondenceto the focus detection areas G1-G5. Namely, focus detection pixel rowson the image sensor 211 sample the image portions in the focus detectionareas G1-G5 within the subject image formed on the photographic imageplane G. It is to be noted that a first focus detection pixel row to beused for high-accuracy focus detection and a second focus detectionpixel row used for large defocusing detection are set within each focusdetection area.

FIG. 3 shows the positional arrangement of color filters disposed at theimage sensor 211. Color filters in a Bayer array, as shown in FIG. 3,are each disposed at one of the imaging pixels arrayed two-dimensionallyon the substrate of the image sensor 211. It is to be noted that whileFIG. 3 shows the color filter positional arrangement corresponding to afour-pixel imaging area, this imaging pixel unit adopting the colorfilter positional arrangement over the four-pixel area istwo-dimensionally reiterated. The imaging pixels each equipped with aprimary color filter corresponding to one of the primary colors R (red),G (green) and B (blue) have sensitivity characteristics such as thoseshown in FIG. 4. In this Bayer array, two pixels each equipped with a Gfilter with sensitivity close to the peak of the relative luminosityshown in FIG. 5 are disposed diagonally across from each other andpixels, one equipped with a B filter and the other with an R filter, aredisposed diagonally across from each other.

It is to be noted that the color filters may be arranged in an arrayother than the Bayer array shown in FIG. 3. For instance, an imagingpixel unit that includes complementary color filters, i.e., a G (green)filter, a Ye (yellow) filter, an Mg (magenta) filter and a Cy (cyan)filter, as shown in FIG. 6, may be reiterated two-dimensionally.

FIG. 7 is a front view showing in detail the structure of the imagesensor 211. It is to be noted that FIG. 7 shows part of the image sensor211, near a given focus detection area set on the image sensor 211, inan enlargement. At the image sensor 211, imaging pixels 310 eachequipped with a color filter corresponding to R, G or B aretwo-dimensionally disposed so as to compose the Bayer array in FIG. 3.In addition, at each of the positions corresponding to the focusdetection areas G1-G5 in FIG. 2, first focus detection pixels 311 usedfor high-accuracy focus detection and second focus detection pixels 312used for large defocusing detection, instead of the imaging pixels 310,are disposed.

FIG. 8 is an enlargement of an imaging pixel 310. The imaging pixel 310includes a micro-lens 10, a photoelectric conversion unit 11 and a colorfilter (not shown). FIG. 9 is an enlargement of a first focus detectionpixel 311. The first focus detection pixel 311 includes a micro-lens 10,a pair of photoelectric conversion units 12 and 13 and a filter (notshown). FIG. 10 is an enlargement of a second focus detection pixel 312.The second focus detection pixel 312 includes a micro-lens 10, a pair ofphotoelectric conversion units 14 and 15 and a filter (not shown).

FIG. 11 shows the characteristics of the filters disposed at the firstfocus detection pixels 311 and the second focus detection pixels 312.These filters are sensitive in the visible light range but are notsensitive in the ultraviolet range and the infrared range. In otherwords, a sufficient quantity of light can be assured with better ease inconjunction with these filters even at low brightness levels. Inaddition, the first focus detection pixels 311 and the second focusdetection pixels 312 have a wider range of wavelength sensitivity thanthe other type of pixels, i.e., the imaging pixels 310, and thus, theirfocus detection performance remains unaffected by the color of thesubject image over the focus detection areas.

As shown in FIG. 8, the photoelectric conversion unit 11 at each imagingpixel 310 is designed in a shape that allows the photoelectricconversion unit to receive all the light flux passing through the exitpupil of the exchangeable lens unit 202 at a light setting, e.g., anexit pupil equivalent to F 1.0, via the micro-lens 10. In addition, thepair of photoelectric conversion units 12 and 13 at each first focusdetection pixel 311 is designed in a shape that allows the photoelectricconversion units to receive all the light flux passing through aspecific exit pupil of the exchangeable lens unit 202, e.g., an exitpupil equivalent to F 2.8, via the micro-lens 10, as shown in FIG. 9.

In addition, as shown in FIG. 10, the pair of photoelectric conversionunits 14 and 15 at each second focus detection pixel 312 are designed ina shape that allows the photoelectric conversion units to receive thelight flux passing through an exit pupil corresponding to a higher Fvalue along the direction in which the photoelectric conversion unitsare set side-by-side, relative to the pair of photoelectric conversionunits 12 and 13 at the first focus detection pixel 311 (e.g., an exitpupil equivalent to F 5.6) via the micro-lens 10.

As shown in FIG. 7, the image sensor 211 includes the imaging pixels 310each equipped with a color filter corresponding to R, G or B arranged soas to reiterate the Bayer array in FIG. 3, and the first focus detectionpixels 311 for high-accuracy focus detection and the second focusdetection pixels 312 for large defocusing detection disposed over anarea corresponding to each of the positions of the focus detection areasG1-G5 shown in FIG. 2. The first focus detection pixels 311 forhigh-accuracy focus detection are densely disposed in a straighthorizontal row (in a vertical row in each of the focus detection areasG4 and G5), which would otherwise be taken up by imaging pixels 310equipped with B filters and G filters, without allowing any intervalsbetween the individual first focus detection pixels.

The second focus detection pixels 312 used for large defocusingdetection, on the other hand, are disposed in close proximity to thefirst focus detection pixels 311 for high-accuracy focus detection, in astraight horizontal row (in a vertical row in each of the focusdetection areas G4 and G5), which would otherwise be taken up by imagingpixels 310 equipped with B filters and G filters, by allowing two-pixelintervals between the individual second focus detection pixels.

It is desirable that the image at a single position in the imaging planeG be sampled via the pixel row made up with the second focus detectionpixels 312 for large defocusing detection and via the pixel row made upwith the first focus detection pixels 311 for high-accuracy focusdetection, so as to improve the focus detection accuracy. From thisviewpoint, it would be ideal to dispose the two pixel rows adjacent toeach other to improve the focus detection accuracy to the maximumextent. However, such a positional arrangement would compromise theaccuracy of interpolation executed to interpolate outputs of the focusdetection pixels based upon the outputs from the imaging pixels presentaround the focus detection pixels. Namely, the positional arrangementwith the two pixel rows set adjacent to each other would lead to asignificant interpolation error. From this perspective, the two pixelrows should be set apart from each other with at least a three-pixelinterval in order to assure better quality for the captured image. Whilethe two pixel rows are set apart from each other over a three-pixelinterval in the example presented in FIG. 7, the two pixel rows can beregarded to sample the image at a single position within the imagingplane since the pixels themselves are extremely small.

The following advantage is obtained by disposing the first focusdetection pixels 311 and the second focus detection pixels 312 along thehorizontal (or vertical) rows that would otherwise be taken up byimaging pixels 310 equipped with B filters and G filters. Namely, evenif a slight error occurs when generating pixel signals at the firstfocus detection pixels 311 and the second focus detection pixels 312through pixel interpolation to be detailed later, the error is more orless unnoticeable to the human eye, since the human eye is moreperceptive to red than to blue, and the green pixels disposed withhigher density compared to the blue pixels and the red pixels have alower defect contribution factor per pixel.

The first focus detection pixels 311 are disposed densely at the centerof each of the focus detection areas (G1-G5), whereas the second focusdetection pixels 312 are disposed more sparsely over a range greaterthan the range of the first focus detection pixels 311. FIGS. 12A and12B show how an image 313 formed on the image sensor 211 is sampled viathe first focus detection pixels 311 and the second focus detectionpixels 312. In FIGS. 12A and 12B the image intensity is indicated alongthe vertical axis and the image distribution is indicated along thehorizontal axis. As shown in FIG. 12A, the image 313 can be detectedwith a fine image detection pitch d1 via the row of the first focusdetection pixels 311. Via the row of the second focus detection pixels312, on the other hand, the image 313 is detected over a wider rangewith an image detection pitch d2, which is larger than the imagedetection pitch corresponding to the row of the first focus detectionpixels 311, as shown in FIG. 12B.

The image detection pitch d2 for the row of the second focus detectionpixels 312 is set larger than the image detection pitch d1 set for therow of the first focus detection pixels 311 for the following reasons.Firstly, since any fine image structure will be blurred when thedefocusing amount is large, it is useless to detect the image with afine image detection pitch. Secondly, since each second focus detectionpixels 312 is surrounded by imaging pixels, image signals can begenerated with better interpolation accuracy to lead to an improvedimage signal quality. Thirdly, since the number of second focusdetection pixels disposed in the row can be reduced by setting theindividual second focus detection pixels with intervals, the focusdetection calculation to be detailed later can be executed on a smallerscale, which, in turn, improves the response in the focus detection. Atthe same time, the second focus detection pixels can be disposed over awide range to enable detection of a large image shift amount.

FIG. 13 is a sectional view of an imaging pixel 310. The micro-lens 10is set to the front of the imaging photoelectric conversion unit 11 atthe imaging pixel 310 and, as a result, an image of the photoelectricconversion unit 11 is projected frontward via the micro-lens 10. Thephotoelectric conversion unit 11 is formed on a semiconductor circuitsubstrate 29, with a color filter (not shown) disposed between themicro-lens 10 and the photoelectric conversion unit 11.

FIG. 14 is a sectional view of a first focus detection pixel 311 or asecond focus detection pixel 312. The reference numerals inside theparentheses in FIG. 14 and in the following description indicatecomponents of the second focus detection pixel 312. In the first focusdetection pixel 311 (second focus detection pixel 312), the micro-lens10 is disposed to the front of the photoelectric conversion units 12 and13 (14 and 15) used for focus detection and thus, images of thephotoelectric conversion units 12 and 13 (14 and 15) are projectedfrontward via the micro-lens 10. The photoelectric conversion units 12and 13 (14 and 15) are formed on the semiconductor circuit substrate 29,with a color filter (not shown) disposed between the micro-lens 10 andthe photoelectric conversion units 12 and 13 (14 and 15).

Next, focus detection executed by adopting a pupil division-type methodis explained in reference to FIG. 15. FIG. 15 shows a micro-lens 50 of afirst focus detection pixel 311 disposed on an optical axis 91 of theexchangeable lens unit 202, a pair of photoelectric conversion units 52and 53 disposed to the rear of the micro-lens 50, a micro-lens 60 of afirst focus detection pixel 311 disposed off the optical axis 91 of theexchangeable lens unit 202, and a pair of photoelectric conversion units62 and 63 disposed to the rear of the micro-lens 60. An exit pupil 90 ofthe exchangeable lens unit 202 is set at a position assumed over adistance d4 to the front of the micro-lenses 50 and 60 disposed on theestimated image forming plane of the exchangeable lens unit 202. Thedistance d4 takes a value determined in correspondence to the curvatureand the refractive index of the micro-lenses 50 and 60, the distancebetween the micro-lenses 50 and 60 and the photoelectric conversionunits 52/53 and 62/63 and the like. In the description, the distance d4is referred to as a range-finding pupil distance.

The micro-lenses 50 and 60 are set at the estimated image-forming planeof the exchangeable lens unit 202. The shapes of the pair ofphotoelectric conversion units 52 and 53 are projected via themicro-lens 50 set on the optical axis 91 onto the exit pupil 90 setapart from the micro-lenses 50 by the projection distance d4 and theprojected shapes define the range-finding pupils 92 and 93. The shapesof the pair of photoelectric conversion units 62 and 63 are projectedvia the micro-lens 60 set off the optical axis 91 onto the exit pupil 90set apart by the projection distance d4 and the projected shapes definerange-finding pupils 92 and 93. Namely, the projecting direction foreach pixel is determined so that the projected shapes (range-findingpupils 92 and 93) of the photoelectric conversion units in theindividual pixels are aligned on the exit pupil 90 set over theprojection distance d4.

The photoelectric conversion unit 52 outputs a signal corresponding tothe intensity of an image formed on the micro-lens 50 with a focusdetection light flux 72 having passed through the range-finding pupil 92and having advanced toward the micro-lens 50. The photoelectricconversion unit 53 outputs a signal corresponding to the intensity of animage formed on the micro-lens 50 with a focus detection light flux 73having passed through the range-finding pupil 93 and having advancedtoward the micro-lens 50. Also, the photoelectric conversion unit 62outputs a signal corresponding to the intensity of an image formed onthe micro-lens 60 with a focus detection light flux 82 having passedthrough the range-finding pupil 92 and having advanced toward themicro-lens 60. The photoelectric conversion unit 63 outputs a signalcorresponding to the intensity of an image formed on the micro-lens 60with a focus detection light flux 83 having passed through therange-finding pupil 93 and having advanced toward the micro-lens 60.

By arranging numerous focus detection pixels each structured asdescribed above in a straight row and integrating the outputs from thepairs of photoelectric conversion units into output groups eachcorresponding to the two range-finding pupils 92 and 93, informationrelated to the intensity distribution of the pair of images formed onthe focus detection pixel row with the individual focus detection lightfluxes passing through the range-finding pupil 92 and the range-findingpupil 93 is obtained. Next, image shift detection arithmetic processing(correlational processing, phase difference detection processing) to bedetailed later is executed by using the information thus obtained so asto detect the image shift between the pair of images through the pupildivision-type detection method. The image shift amount is thenmultiplied by a predetermined conversion coefficient and, as a result,the extent of deviation (defocus amount) of the current image formingplane (the image forming plane on which the image is formed at the focusdetection position corresponding to a specific micro-lens array positionon the estimated image forming plane) relative to the estimated imageforming plane can be calculated. It is to be noted that the accuracywith which the defocus amount (image shift amount) is detected isdetermined in correspondence to the image detection pitch set for theimage shift amount detection and the opening angle formed with thegravitational centers of the range-finding pupils.

It is to be noted that FIG. 15 schematically shows the first focusdetection pixel (the micro-lens 50 and the pair of photoelectricconversion units 52 and 53) disposed on the optical axis 91 and theadjacent first focus detection pixel (the micro-lens 60 and the pair ofphotoelectric conversion units 62 and 63). At each of the other focusdetection pixels, too, the light fluxes arriving at the micro-lens fromthe pair of range-finding pupils are received at the pair ofphotoelectric conversion units.

FIG. 16 is a front view showing the relationship between the projectionranges (range-finding pupils) over which the pair of photoelectricconversion units 12 and 13 in a first focus detection pixel 311 areprojected on the exit pupil 90 of the exchangeable lens unit 202. Acircle circumscribing the range-finding pupils 92 and 93 (indicated bythe solid lines) formed by projecting the pair of photoelectricconversion units 12 and 13 (see FIG. 9) in the first focus adjustmentpixel 311 onto the exit pupil plane 90 via the micro-lens 10, as viewedfrom the estimated image forming plane, assumes a specific opening Fvalue (range-finding pupil F value).

A circle 94 indicated by the dotted line in FIG. 16 is the outer edge ofthe exit pupil 90 of the exchangeable lens unit 202. In addition, points95 and 96 indicate the positions of the gravitational centers of therange-finding pupils 92 and 93 along the direction in which therange-finding pupils 92 and 93 are set side-by-side. In correspondenceto the opening angle formed by viewing the two gravitational centerpositions 95 and 96 (the distance w3) from the focus detection position,the value of the conversion coefficient used to convert the image shiftamount to the defocus amount is determined. The focus detection accuracyimproves as the opening angle increases, whereas the defocus amountdetection range increases as the opening angle becomes smaller (theimage shift amount corresponding to a given defocus amount is smaller).

In the example presented in FIG. 16, the pair of range-finding pupils 92and 93 are semicircles set so as to achieve a lateral symmetry. Thewidth w1 over which the pair of range-finding pupils 92 and 93 rangealong the direction in which they are set side-by-side is substantiallyequal to the height h1 of the range-finding pupils 92 and 93 measuredalong the direction perpendicular to the direction in which therange-finding pupils are set side-by-side. In addition, w2 indicates thewidth of each range-finding pupil 92 and 93 measured along the directionin which the range-finding pupils 92 and 93 are set side-by-side. Whenthe width w2 is large, defocusing results in a significant extent ofimage blur.

FIG. 17 is a front view showing the relationship between the projectionranges (range-finding pupils) over which the pair of photoelectricconversion units 14 and 15 in a second focus detection pixel 312 areprojected on the exit pupil 90 of the exchangeable lens unit 202. Byprojecting the pair of photoelectric conversion units 14 and 15 (seeFIG. 10) in the second focus adjustment pixel 312 onto the exit pupilplane 90 via the micro-lens 10, range-finding pupils 97 and 98(indicated by the solid lines) of the second focus detection pixel 312are formed.

The circle 94 indicated by the dotted line in FIG. 17 is the outer edgeof the exit pupil 90 of the exchangeable lens unit 202. In addition,points 99 and 100 indicate the positions of the gravitational centers ofthe range-finding pupils 97 and 98 along the direction in which therange-finding pupils are set side-by-side. The opening angle formed byviewing the gravitational center positions 99 and 100 (the distance w6)from the focus detection position is smaller than the opening angleformed in correspondence to the first focus detection pixel 311, and theconversion coefficient, determined in correspondence to this openingangle to be used to convert the image shift amount to the defocusamount, too, assumes a smaller value. Namely, the second focus detectionpixels 312 are optimized for large defocusing detection.

For instance, in the example presented in FIG. 18 with reference numeral101 indicating the image sensor surface, reference numeral 102indicating the image forming plane and d5 indicating the defocus amountat the image sensor surface 101, the image shift S1 at the image sensorsurface 101 is determined in correspondence to the angle formed byviewing the gravitational center positions 95 and 96 on the exit pupil90 through focus detection executed via the pixel row of the first focusdetection pixels 311. In addition the image shift S2 (S2<S1) at theimage sensor surface 101 is determined in correspondence to the angleformed by viewing the gravitational center positions 99 and 100 on theexit pupil 90 through focus detection executed via the pixel row of thesecond focus detection pixels 312. As long as the image shift amount issmall, the focus detection pixel row does not need to be long.

In addition, the pair of range-finding pupils 97 and 98 in FIG. 17 arerectangles set so as to achieve line symmetry. The width w4 over whichthe range-finding pupils 97 and 98 range along the direction in whichthey are set side-by-side is smaller than the width w1 (see FIG. 16)over which the range-finding pupils 92 and 93 in correspondence to thefirst focus detection pixel 311, range along the direction in which theyare set side-by-side. The height h2 of the range-finding pupils 97 and98 measured along the direction perpendicular to the direction in whichthe range-finding pupils 97 and 98 are set side-by-side is equal to orgreater than the height h1 (see FIG. 16) of the range-finding pupils 92and 93 measured along the direction perpendicular to the direction alongwhich they are set side-by-side in correspondence to the first focusdetection pixel 311. The width w5 of either the range-finding pupil 97or 98 (range-finding pupil 97 in this example) measured along thedirection in which the range-finding pupils 97 and 98 are setside-by-side is set smaller than the width w2 (see FIG. 16) of eitherthe range-finding pupil 92 or 93 (range-finding pupil 92 in this case)measured along the direction in which the range-finding pupils 92 and 93are set side-by-side in correspondence to the first focus detectionpixel 311. Thus, even a large extent of defocusing does not lead to asignificant image blur and highly accurate image shift detection can beexecuted by using a high contrast image.

FIGS. 19A, 19B and 19C show the distributions of the image intensitydetected by varying the width of one of the range-finding pupilsmeasured along the direction in which the range-finding pupils are setside-by-side from a small setting to an intermediate setting and a largesetting relative to a given large defocusing amount (relative to a givenimage shift amount). The direction in which the range-finding pupils areset side-by-side is the direction in which the range-finding pupils 92and 93 are set side-by-side in FIG. 16. In this case, the width of oneof the range-finding pupils is W2. In addition, the width of one of therange-finding pupils, taken along the direction in which therange-finding pupils 97 and 98 are set side-by-side in FIG. 17, is W5.If the width of the range-finding pupil measured along the direction inwhich the two range-finding pupils are set side-by-side is large, a fineimage structure becomes blurred, resulting in an image containing a lowfrequency component alone, and in such a case, accurate image shiftdetection cannot be executed with ease or the image shift detectionitself may become disabled. If, on the other hand, the width of one ofthe range-finding pupils, measured along the direction in which therange-finding pupils are set side-by-side, is small, the fine imagestructure will be retained even if there is defocusing, enablingaccurate image shift detection.

By setting the height h2 of the range-finding pupils 97 and 98 measuredalong the direction perpendicular to the direction in which therange-finding pupils 97 and 98 are set side-by-side, to a value greaterthan the width w4 over which the range-finding pupils 97 and 98 rangealong the direction in which they are set side-by-side, a sufficientquantity of light can be obtained for large defocusing detection and adesired level of focus detection performance can be maintained even atlow brightness levels.

FIG. 20 presents a flowchart of the operations executed in the digitalstill camera (imaging device) shown in FIG. 1. The camera drive controldevice 212 repeatedly executes the processing in step S110 andsubsequent steps after power is turned on at the camera body 203 in stepS100. In step S110, data are read out from the pixel row of the firstfocus detection pixels 311 and the pixel row of second focus detectionpixels 312. It is assumed that the photographer has selected in advancea specific focus detection area by operating an operation member viawhich focus detection area is selected. In step S120, image shiftdetection calculation processing is executed based upon pairs of sets ofimage data, one pair corresponding to the pixel row of the first focusdetection pixels 311 and the other pair corresponding to the pixel rowof the second focus detection pixels 312, to calculate the image shiftamount.

The image shift detection calculation processing (correlationalalgorithm) is now explained in reference to FIG. 22. A correlationquantity C(L) is first calculated by using the differentialcorrelational algorithm expressed in (1) below, with ei and fi (i=1 tom) representing the pair of sets of data corresponding to each focusdetection pixel row.

C(L)=Σ|e(i+L)−f(i)|  (1)

L in expression (1) is an integer representing the relative shift amountindicated in units corresponding to the pitch at which the pair of setsof data are detected. In addition, L assumes a value within a range Lminto Lmax (−5 to +5 in the figure). Σ indicates total sum calculation overa range expressed as i=p to q, with p and q satisfying a conditionalexpression 1≦p<q≦m. The specific values assumed for p and q define thesize of the focus detection area.

As shown in FIG. 22A, the results of the calculation executed asexpressed in (1) indicate the smallest correlation quantity C(L) incorrespondence to the shift amount L=kj (kj=2 in FIG. 22A) indicating ahigh level of correlation between the pair of sets of data. Next, ashift amount x, which will provide the minimum value C(L)min=C(x) in acontinuous curve representing the correlation quantities, is determinedthrough the three-point interpolation method as expressed in (2) to (5)below.

x=kj+D/SLOP   (2)

C(x)=C(kj)−|D|  (3)

D={C(kj−1)−C(kj+1)}/2   (4)

SLOP=MAX{C(kj+1)−C(kj), C(kj−1)−C(kj)}  (5)

In addition, a defocus amount DEF representing the extent of defocusingof the subject image plane relative to the estimated image forming planecan be determined as expressed in (6) below based upon the shift amountx having been calculated as expressed in (2).

DEF=KX·PY·x   (6)

PY in expression (6) represents the detection pitch, whereas KX inexpression (6) represents the conversion coefficient that is determinedin correspondence to the opening angle formed with the gravitationalcenters of the pair of range-finding pupils.

The judgment as to whether or not the calculated defocus amount DEF isreliable is made as follows. As shown in FIG. 22B, the interpolatedminimum value C(X) of the correlation quantity increases when the levelof correlation between the pair of sets of data is low. Accordingly, ifC(X) is equal to or greater than a predetermined value, the defocusamount is judged to be less reliable. Alternatively, C(X) may bestandardized with regard to the data contrast, and in such a case, ifthe value obtained by dividing C(X) by SLOP indicating a value inproportion to the contrast is equal to or greater than a predeterminedvalue, the defocus amount should be judged to be not reliable. As afurther alternative, if SLOP indicating the value in proportion to thecontrast is equal to or less than a predetermined value, the subjectshould be judged to be a low contrast subject and, accordingly, thereliability of the calculated defocus amount DEF should be judged to below.

It is to be noted that if the level of correlation between the pair ofsets of data is low and the correlation quantity C(L) does not dip atall over the shift range Lmin to Lmax, as shown in FIG. 22C, the minimumvalue C(X) cannot be determined. Under such circumstances, it is judgedthat the focus detection is disabled.

FIG. 21 presents a flowchart of the image shift amount detectionoperation executed in step S120 in FIG. 20. After starting the imageshift amount detection operation in step S300, correlational shiftcalculation is executed on the pair of sets of data over a predeterminedshift range in step S310. In step S320, a decision is made as to whetheror not there is a minimal point with which three-point interpolationcalculation can be executed. If it is decided that there is no suchminimal point, the operation proceeds to step S360. In step S360, it isjudged that image shift detection is not possible (disabled focusdetection), before the operation makes a return from step S370.

If, on the other hand, it is decided in step S320 that there is aneligible minimal point, the operation proceeds to step S330 tointerpolate the maximum correlational quantity at a point close to thecorrelation quantity indicating the highest extent of correlation. Instep S340 following step S330, the reliability of the maximumcorrelation quantity is judged. If it is decided that the maximumcorrelation quantity is not reliable, image shift detection is judged tobe not possible (disabled focus detection) in step S360 before theoperation makes a return from step S370. If, on the other hand, it isdecided that the maximum correlation quantity is reliable, the operationproceeds to step S350 to designate the shift amount corresponding to themaximum correlation quantity as the image shift amount and then theoperation makes a return from step S370.

In step S130 in FIG. 20, to which the operation makes a return, adecision is made as to whether or not the image shift detectioncalculation has been executed with success by using the first focusdetection pixel row data, i.e., whether or not the focus can be detectedby using the first focus detection pixel row data. If it is decided thatthe focus detection is possible, the operation proceeds to step S140 toconvert the image shift amount indicated in the results of thecalculation executed by using the first focus detection pixel row datato the defocus amount, and then the operation proceeds to step S180.

If, on the other hand, it is decided in step S130 that the focusdetection is not possible, the operation proceeds to step S150. In stepS150, a decision is made as to whether or not the image shift detectioncalculation has been successfully executed by using the second focusdetection pixel row data, i.e., whether or not the focus can be detectedby using the second focus detection pixel row data. If it is decidedthat the focus detection is possible, the operation proceeds to stepS160 to convert the image shift amount indicated in the results of thecalculation executed by using the second focus detection pixel row datato the defocus amount and then the operation proceeds to step S180.

If it is decided in step S150 that the focus detection is not possible,the operation proceeds to step S170. In step S170, an instruction (scandrive instruction) for the CPU (not shown) in the lens drive controldevice 209 to drive the focusing lens toward the infinity side or theclose-up side by a specific extent is transmitted, and the operationthen returns to step S110. Upon receiving the scan drive instruction,the lens drive control device 209 drives the focusing lens 207 by thespecific extent toward the infinity side or the close-up side.

In step S180, a decision is made as to whether or not the absolute valueof the calculated defocus amount is equal to or less than apredetermined value, i.e., whether or not the focusing lens 207 is setat a point near the focus match position. If the absolute value of thedefocus amount is not equal to or less than the predetermined value, theoperation proceeds to step S190. In step S190, the defocus amount istransmitted to the CPU in the lens drive control device 209 so as toenable the lens drive control circuit to drive the focusing lens 207 inthe exchangeable lens unit 202 to the focus match position. Once theprocessing in step S190 ends, the operation returns to step S110 torepeatedly execute the operations described above.

If it is decided in step S180 that the absolute value of the defocusamount is equal to or less than the predetermined value, the operationproceeds to step S200. In step S200, a decision is made as to whether ornot a shutter release has been executed through an operation at ashutter release button (not shown). If it is decided that a shutterrelease has not been executed, the operation returns to step S110 torepeatedly execute the operations described above. If, on the otherhand, it is decided that a shutter release has been executed, theoperation proceeds to step S210 to read out the image signals from theimaging pixels at the image sensor 211.

In step S220 following step S210, a pixel signal at each of the pixelsof the first focus detection pixel row and the second focus detectionpixel row is obtained through interpolation by using the signals fromthe surrounding imaging pixels. In step S230 following step S220, theimage signals are saved into the memory card 213. Subsequently, theoperation returns to step S110 to repeatedly execute the operationsdescribed above.

A pixel signal at each of the pixels of the first focus detection pixelrow is interpolated as explained below based upon the signals from thesurrounding imaging pixels. FIG. 23 shows the positional arrangementwith regard to the first focus detection pixel row (AF1-AF5) and thesurrounding imaging pixels (blue pixels B1-B6, red pixels R1-R4 andgreen pixels G1-G10). With J (AF2) indicating the output of the focusdetection pixel AF2 set at a position that would otherwise be taken upby a green pixel and I(G3), I(G4), I (G6) and I (G7) indicating theoutputs from the surrounding green pixels, a pixel output I(AF2) at theposition assumed by the focus detection pixel AF2 is expressed as in (7)below.

I(AF2)=(I(G3)+I(G4)+I(G6)+I(G7))/4   (7)

Alternatively, I(AF2) may be calculated as in expression (8) below bytaking into consideration the output J (AF2) from the focus detectionpixel AF2.

I(AF2)=(I(G3)+I(G4)+I(G6)+I(G7)+k1×J(AF2))/5   (8)

k1 in expression (8) represents a coefficient used for sensitivityadjustment.

With J (AF3) indicating the output of the focus detection pixel AF3 setat a position that would otherwise be taken up by a blue pixel and I(B2)and I(B5) indicating the outputs from the surrounding blue pixels, thepixel output I (AF3) at the position assumed by the focus detectionpixel AF3 is expressed as in (9) below.

I(AF3)=(I(B2)+I(B5))/2   (9)

Alternatively, I(AF3) may be calculated as in expression (10) below bytaking into consideration the output J (AF3) of the focus detectionpixel AF3.

I(AF3)=(I(B2)+I(B5)+k2×J(AF3))/3   (10)

k2 in expression (10) represents a coefficient used for sensitivityadjustment.

A pixel signal at each of the pixels in the second focus detection pixelrow, too, is obtained through interpolation based upon the pixel signalsoutput from the surrounding imaging pixels. However, the quality of thepixel signal obtained through interpolation at a position that wouldotherwise be taken up by a blue pixel is improved over the quality ofthe pixel signal expressed in (9) or (10), since it can be interpolatedby using the outputs from the blue pixels present along the direction inwhich the focus detection pixels are arrayed, as well.

(Variations of Image Sensors)

At the image sensor 211 shown in FIG. 7, the first focus detectionpixels 311 for high-accuracy focus detection are disposed denselywithout allowing any intervals and the second focus detection pixels 312for large defocusing detection are disposed with two-pixel intervals. Atan image sensor 211A shown in FIG. 24, the first focus detection pixels311 for high-accuracy focus detection are set with a one-pixel intervaland the second focus detection pixels 312 for large defocusing detectionare each disposed at every fourth pixel position.

The quality of an image obtained by the image sensor 211A in thevariation shown in FIG. 24 is improved, since the first focus detectionpixels 311 for high-accuracy focus detection at the image sensor 211Aare disposed with one-pixel intervals and thus the interpolation errorbecomes less noticeable compared to that at the image sensor 211 shownin FIG. 7. It is to be noted that the first focus detection pixels 311for high-accuracy focus detection are set at positions that wouldotherwise be taken up by imaging pixels equipped with B filters at theimage sensor 211A in FIG. 24. However, a similar advantage will beachieved by disposing the first focus detection pixels at positions thatwould otherwise be taken up by pixels equipped with G filters.

In addition, while the focus detection pixels 311 and 312 shown in FIGS.9 and 10 each include a pair of photoelectric conversion units (12, 13)or (14, 15), focus detection may also be executed by using focusdetection pixels each equipped with a single photoelectric conversionunit instead of a pair of photoelectric conversion units. For instance,instead of the first focus detection pixels 311 for high-accuracy focusdetection shown in FIG. 9, first focus detection pixels 313 and 314 forhigh-accuracy focus detection shown in FIGS. 25A and 25B may bealternately arrayed to enable focus detection. The focus detection pixel313 in FIG. 25A includes a single photoelectric conversion unit 16 whichcorresponds to the photoelectric conversion unit 13 in FIG. 9. The focusdetection pixel 314 in FIG. 25B includes a single photoelectricconversion unit 17 which corresponds to the photoelectric conversionunit 12 in FIG. 9.

The pair of range-finding pupils formed by projecting the photoelectricconversion units 16 and 17 in FIGS. 25A and 25B via the micro lenses 10do not overlap each other, as shown in FIG. 16. However, thephotoelectric conversion units may instead assume shapes such as thoseshown in FIGS. 26A and 26B so as to allow the pair of range-findingpupils, formed by projecting them onto the exit pupil via the microlenses 10, to partially overlap each other. With such photoelectricconversion units, a sufficient quantity of light can be obtained moreeasily and thus, the focus detection performance at low brightnesslevels can be improved. The focus detection pixel 317 in FIG. 26Aincludes a single photoelectric conversion unit 20 ranging beyond thecentral line 22 of the pixel, whereas the focus detection pixel 318 inFIG. 26B includes a single photoelectric conversion unit 21 rangingbeyond the central line 23 of the pixel.

In addition, instead of the second focus detection pixels 312 for largedefocusing detection shown in FIG. 10, second focus detection pixels 313and 314 for large defocusing detection shown in FIGS. 27A and 27B may bealternately arrayed to enable focus detection. The focus detection pixel315 in FIG. 27A includes a single photoelectric conversion unit 18 whichcorresponds to the photoelectric conversion unit 15 in FIG. 10. Thefocus detection pixel.316 in FIG. 27B includes a single photoelectricconversion unit 19, which corresponds to the photoelectric conversionunit 14 in FIG. 10.

FIG. 28 shows an image sensor 211B that includes second focus detectionpixels constituted with the focus detection pixels 315 and 316 shown inFIGS. 27A and 27B. FIG. 29 shows an image sensor 211C that includesfirst focus detection pixels constituted with the focus detection pixels313 and 314 shown in FIGS. 25A and 25B and second focus detection pixelsconstituted with the focus detection pixels 315 and 316 shown in FIGS.27A and 27B. It is to be noted that the image is detected via the focusdetection pixels 313 and 314 with a detection pitch corresponding to atwo-pixel unit and the image is detected via the focus detection pixels315 and 316 with a detection pitch corresponding to a six-pixel unit atthe image sensor shown in FIG. 29.

The image sensor 211C in FIG. 29 assumes a simpler structure than theimage sensor 211 in FIG. 7 with a pair of photoelectric conversion unitsinstalled at each pixel, and thus, the image sensor 211C can bemanufactured with greater ease at lower cost.

At the image sensor 211 shown in FIG. 7, two rows of focus detectionpixels, i.e., the first focus detection pixel row with a finer imagedetection pitch and the second focus detection pixel row with a largeimage detection pitch, are set parallel to each other in each focusdetection area. As an alternative, a pixel row with a larger imagedetection pitch may be attached at an end of the first focus detectionpixel row. FIG. 30 shows an image sensor 211D with first focus detectionpixels 311 set densely without allowing any intervals at the center ofthe focus detection area and first focus detection pixels 311 disposedtoward the periphery of the focus detection area so as to take up everyother pixel position. The output from the pixel row at the center, madeup with the densely set first focus detection pixels 311, is used forhigh-accuracy focus detection, whereas the outputs from every otherfirst focus detection pixel 311 over the central area and the outputsfrom the peripheral first focus detection pixels 311 are used for largedefocusing detection.

The image sensor 211D shown in FIG. 30 with a smaller number of focusdetection pixels overall compared to the image sensor 211 shown in FIG.7, which includes two rows of focus detection pixels in each focusdetection area, provides a higher quality image.

While the image sensor 211 in FIG. 7 includes imaging pixels equippedwith color filters set so as to achieve a Bayer array, the structure ofthe color filters and the color filter array of the color filters arenot limited to those in this example. FIG. 31 shows an image sensor 211Eequipped with complementary-color filters (green G, yellow Ye, magentaMg and cyan Cy), which are two-dimensionally arrayed as shown in FIG. 6.At this image sensor, the first focus detection pixels 311 and thesecond focus detection pixels 312 are disposed at positions that wouldotherwise be occupied by pixels with cyan Cy filters and magenta Mgfilters (colors that contain a blue component with which the outputerror is relatively unnoticeable).

While the range-finding pupils formed with the first focus detectionpixels used for high-accuracy detection and the range-finding pupilsformed with the second focus detection pixels used for large defocusingdetection do not match each other in size at the image sensor 211 shownin FIG. 7, range-finding pupils with matching sizes may be formed,instead.

While the pupil division-type method with micro lenses is explainedabove in reference to the embodiment and its variations, the presentinvention is not limited to applications adopting the pupildivision-type method with micro lenses, and it may be equallyeffectively adopted in a pupil division-type method with polarizationfilters. The following is an explanation of such an application.

FIG. 32 illustrates the concept of a pupil division-type method withpolarization filters. FIG. 32 schematically shows four pixels adjacentto one another. Reference numeral 690 in the figure indicates a holdingframe for polarization filters, with the area that is not taken up bythe polarization filters shielded from light. Reference numeral 692indicates a polarization filter, which forms a range-finding pupil incorrespondence to the position and the shape assumed by the filter.Reference numeral 693 indicates a polarization filter, which forms arange-finding pupil in correspondence to the position and the shape ofthe filter, and its polarizing direction is perpendicular to that of thepolarization filter 692. Reference numeral 91 indicates the optical axisof the exchangeable lens. Reference numeral 621 indicates a polarizationfilter, the polarizing direction of which matches that of thepolarization filter 692. Reference numeral 622 indicates a polarizationfilter, the polarizing direction of which matches that of thepolarization filter 693. Reference numerals 611 and 612 each indicate aphotoelectric conversion unit. Reference numeral 631 indicates a type-Ipixel, whereas reference numeral 632 indicates a type-II pixel. It is tobe noted that reference numerals 672, 673, 682 and 683 each indicate alight flux.

The pixel 631, where the light fluxes having passed through therange-finding pupil formed by the polarization filter 692 are receivedat the photoelectric conversion unit 611 through the polarization filter621, outputs a signal indicating the intensity of the image formed withthe light flux 672 or 682. The pixel 632, where the light fluxes havingpassed through the range-finding pupil formed by the polarization filter693 are received at the photoelectric conversion unit 612 through thepolarization filter 622, outputs a signal indicating the intensity ofthe image formed with the light flux 673 or 683.

By disposing numerous type-I pixels and type-II pixels equipped withpolarization filters as described above along a straight line andintegrating the outputs from the photoelectric conversion units of theindividual pixels into output groups each corresponding to one of therange-finding pupils, information related to the distribution of theintensity of the pair of images formed on the pixel row with focusdetection light fluxes passing through the two range-finding pupils canbe obtained. By executing image shift detection calculation processing(correlational arithmetic processing and phase-difference detectionprocessing) on this information, the extent of image shift between thepair of images can be detected through the pupil division-typephase-difference detection method.

As described above, the image sensor in the embodiment includes a firstfocus detection pixel group and a second focus detection pixel grouprespectively made up with a plurality of first focus detection pixels311, 313, 314, 317, 318 and a plurality of second focus detection pixels312, 315, 316, both used to detect the focus adjustment state at theexchangeable lens unit 202 through the pupil division-type method byreceiving image light fluxes through the exchangeable lens unit 202, inaddition to the imaging pixels 310 each used to convert the image formedthrough the exchangeable lens unit 202 to an image signal. Since theimage detection pitch set for the first focus detection pixel group andthe image detection pitch set for the second focus detection pixel groupat this image sensor are different from each other, both high-accuracyfocus detection and large defocus amount detection can be obtained atthe same time while assuring a high image quality for the capturedimage.

In the embodiment, the pitch with which the first focus detection pixels311, 313, 314, 317, 318 are set in the first focus detection pixel groupand the pitch with which the second focus detection pixels 312, 315, 316are set in the second focus detection pixel group are different fromeach other (see FIGS. 7, 24, 28, 29, 30 and 31). Thus, large defocusamount detection is enabled via the pixel row with a large (coarse)pixel pitch and, at the same time, high-accuracy focus detection isenabled via the pixel row with a small (fine) pixel pitch.

In the embodiment, the second focus detection pixel group assumes agreater length than the first focus detection pixel group (see FIGS. 7and 24). Thus, large defocus amount detection is enabled via the secondfocus detection pixel group with a greater length and, at the same time,high-accuracy focus detection is enabled via the first focus detectionpixel group with a smaller length.

In the embodiment, the pixels in the first focus detection pixel groupand the pixels in the second focus detection pixel group are set alongmatching array directions (see FIGS. 7, 24, 28, 29, 30 and 31). Thus,large defocus amount detection is obtained via one of the pixel rows andat the same time, high-accuracy focus detection is enabled via the otherpixel row, along a given direction in which the subject image ranges.

In the embodiment, the first focus detection pixel group and the secondfocus detection pixel group are disposed in close proximity to eachother (see FIGS. 7, 24, 28, 29, 30 and 31). Thus, large defocus amountdetection is enabled via one of the pixel groups and at the same time,high-accuracy focus detection is enabled via the other pixel group at asubstantially single position within the imaging plane.

In an embodiment, at an end of the first focus detection pixel group, aplurality of first focus detection pixels are disposed with an imagedetection pitch larger than the image detection pitch set for the firstfocus detection pixel group and the two different array patterns are seton a single straight line. Thus, large defocus amount detection isenabled via the two pixel groups and at the same time, high-accuracyfocus detection is enabled via the first focus detection pixel grouppresent at the center, along a given direction in which the subjectimage ranges at a substantially single position within the imagingplane.

In the embodiment, pixels with varying levels of color sensitivity aretwo-dimensionally arrayed by adopting a specific rule and the firstfocus detection pixel group and the second focus detection pixel groupare formed within the two-dimensional pixel array over areas containingpixels with color sensitivity with a low level of the luminosity. Byforming the focus detection pixel groups over the areas containingpixels with color sensitivity with a low level of luminosity, to whichthe human eye does not readily react, any error that may occur whenobtaining outputs from the focus detection pixels through interpolationcan be made less noticeable to the human eye.

In the embodiment, the image sensor is constituted with a plurality ofimaging pixels sensitive to red, green and blue, disposed in a Bayerarray, with the first focus detection pixel group and the second focusdetection pixel group disposed along horizontal or vertical rows thatwould otherwise contain imaging pixels sensitive to blue and greenwithin the two-dimensional imaging pixel array. Since the human eyediscerns red more easily than blue and the green pixels, disposed withhigher density compared to the blue pixels or the red pixels, have asmaller defect contribution factor per pixel, a slight error occurringwhen generating image signals at positions taken up by the first focusdetection pixels and the second focus detection pixels through pixelinterpolation can be made less noticeable to the human eye.

The first focus detection pixels and the second focus detection pixelsin the embodiment with sensitivity over a wider wavelength rangecompared to the non-focus detection pixels, i.e., the imaging pixels.Since this assures a sufficient quantity of light even at low brightnesslevels, the focus detection performance is not affected by the color ofthe subject image in the focus detection area.

In an embodiment, the first focus detection pixels and the second focusdetection pixels each detect a pair of images formed with a pair oflight fluxes passing through a pair of areas at the exit pupil of theexchangeable lens unit 202 and thus, accurate focus detection can beexecuted through the pupil division-type method.

In an embodiment, the pair of images formed with a pair of light fluxespassing through a pair of areas at the exit pupil of the exchangeablelens unit 202 are detected via a plurality of first focus detectionpixels 313 and 314 (see FIGS. 25 and 29). In addition, the pair ofimages formed with a pair of light fluxes passing through a pair ofareas at the exit pupil of the exchangeable lens unit 202 are detectedvia a plurality of second focus detection pixels 315 and 316 (see FIGS.27, 28 and 29). While at least a pair of photoelectric conversion unitsneed to be installed at each focus detection pixel to allow the pair ofimages formed with the pair of light fluxes passing through the pair ofareas at the exit pupil of the exchangeable lens unit 202 to be receivedat a single focus detection pixel, each focus detection pixel only needsto be equipped with, at least, a single photoelectric conversion unit ifthe pair of images are to be received with a plurality of focusdetection pixels. Such an image sensor will assume a simpler structurecompared to an image sensor having a pair of photoelectric conversionunits installed in each pixel, which makes it possible to manufacturethe image sensor with more ease at lower cost.

In an embodiment, the photoelectric conversion units are formed so as topartially overlap the pair of areas formed at the exit pupil of theexchangeable lens unit 202 (see FIG. 26). With focus detection pixelsallowed to receive a greater quantity of light with the photoelectricconversion units formed as described above, better focus detectionperformance at low brightness levels is assured.

In an embodiment, the distance between the gravitational centers of thepair of areas at the exit pupil of the exchangeable lens unit 202 formedin correspondence to the first focus detection pixels and the distancebetween the gravitational centers at the pair of areas at the exit pupilformed in correspondence to the second focus detection pixels do notmatch. By setting a greater distance between the gravitational centersof the pair of areas defined at the exit pupil of the exchangeable lensunit 202 via focus detection pixels, the focus detection accuracy can beraised, whereas a greater defocus amount detection range can be assuredby setting a smaller distance between the gravitational centers.Accordingly, the two types of focus detection pixel groups can beselectively used to better suit specific situations, e.g., focusdetection may be first executed to detect a large defocus amount via thefocus detection pixel group with the smaller gravitational centerinterval and then, once the exchangeable lens unit 202 is driven to apoint near the focus match position, more precise focus detection may beexecuted via the focus detection pixel group with the greatergravitational center interval. Through such optimized use of the twotypes of focus detection pixel groups, high-accuracy focus detection andlarge defocus amount detection can be realized at the same time whileassuring a high image quality for the captured image.

In an embodiment, the distance between the gravitational centers of thepair of areas at the exit pupil of the exchangeable lens unit 202corresponding to the second focus detection pixels is set shorter thanthe distance between the gravitational centers at the pair of areas atthe exit pupil of the exchangeable lens unit 202 corresponding to thefirst focus detection pixels and also a larger image detection pitch isset for the second focus detection pixel group than the image detectionpitch set for the first focus detection pixel group. In this case,high-accuracy focus detection is enabled via the first focus detectionpixel group and focus detection for detecting a large defocus amount isenabled via the second focus detection pixel group. Thus, the focusdetection may be first executed to detect a large defocus amount via thesecond focus detection pixel group and then, once the exchangeable lensunit 202 is driven to a point near the focus match position, moreprecise focus detection may be executed via the first focus detectionpixel group. Through such optimized use of the two types of focusdetection pixel groups, high-accuracy focus detection and large defocusamount detection can be realized at the same time while assuring a highimage quality for the captured image.

In an embodiment, the width over which the pair of areas at the exitpupil at the exchangeable lens unit 202, corresponding to the secondfocus detection pixels, range along the direction in which the pupilsare set side-by-side, is set smaller than the width over which the pairof areas at the exit pupil of the exchangeable lens unit 202,corresponding to the first focus detection pixels, range along thedirection in which the pupils are set next to each other. When therange-finding pupils range over a great width measured along thedirection in which they are set side-by-side, fine image structures inthe subject image become blurred, resulting in an image containing a lowfrequency component alone, which makes it difficult to execute accurateimage shift detection or may even disable the image shift detectionitself. If, on the other hand, the range-finding pupils range over asmaller width measured along the direction in which the pupils are setside-by-side, fine image structures will be retained even in the eventof defocusing and thus, accurate image shift detection is enabled (seeFIG. 16). As a result, less blurring of the subject image will occur asfocus detection is executed to detect a large defocus amount via thesecond focus detection pixel group, and consequently, a highly accurateimage shift detection is enabled by using a high contrast image.

1. An image sensor comprising: imaging pixels that convert an image formed via an optical system to image signals; and a first focus detection pixel group and a second focus detection pixel group respectively made up with an array of first focus detection pixels and an array of second focus detection pixels, with the first focus detection pixels and the second focus detection pixels used to receive an image light flux via the optical system to detect a focus adjustment state at the optical system through a pupil division-type method, wherein: an image detection pitch with which the image is detected via the first focus detection pixel group and an image detection pitch with which the image is detected via the second focus detection pixel group are different from each other.
 2. An image sensor according to claim 1, wherein: an array pitch at which the first focus detection pixels are disposed in the first focus detection pixel group and an array pitch at which the second focus detection pixels are disposed in the second focus detection pixel group are different from each other.
 3. An image sensor according to claim 1, wherein: the second focus detection pixel group ranges over a greater length than the first focus detection pixel group.
 4. An image sensor according to claim 1, wherein: an array direction of the first focus detection pixel group and an array direction of the second focus detection pixel group match each other.
 5. An image sensor according to claim 1, wherein: the first focus detection pixel group and the second focus detection pixel group are set in close proximity to each other.
 6. An image sensor according to claim 1, wherein: the first focus detection pixel group and the second focus detection pixel group are set along a single straight line.
 7. An image sensor according to claim 6, wherein: the second focus detection pixel group is disposed at an end of the first focus detection pixel group.
 8. An image sensor according to claim 1, wherein: the first focus detection pixels and the second focus detection pixels have sensitivity over a wider wavelength range than pixels other than the first focus detection pixels and the second focus detection pixels.
 9. An image sensor according to claim 1, wherein: the first focus detection pixels and the second focus detection pixels are each constituted with a micro-lens and a photoelectric conversion unit.
 10. An image sensor according to claim 1, wherein: the first focus detection pixels and the second focus detection pixels each detect a pair of images formed with light fluxes passing through a pair of areas at an exit pupil of the optical system.
 11. An image sensor according to claim 10, wherein: the photoelectric conversion unit is formed so as to allow the pair of areas at the exit pupil of the optical system to partially overlap.
 12. An image sensor according to claim 10, wherein: an interval between gravitational centers of the pair of areas at the exit pupil of the optical system, which corresponds to the first focus detection pixels, and an interval between gravitational centers of the pair of areas at the exit pupil of the optical system, which corresponds to the second focus detection pixels, are different from each other.
 13. An image sensor comprising: an imaging pixel group made up with pixels that convert an image formed via an optical system to image signals, formed by arraying a plurality of pixel sets each constituted with a plurality of pixels with sensitivity to different colors; and a first focus detection pixel group and a second focus detection pixel group respectively made up with an array of first focus detection pixels and an array of second focus detection pixels, with the first focus detection pixels and the second focus detection pixels used to receive an image light flux via the optical system to detect a focus adjustment state at the optical system through a pupil division-type method, wherein: an image detection pitch with which the image is detected via the second focus detection pixel group is larger than an image detection pitch with which the image is detected via the first focus detection pixel group; and the first focus detection pixel group and the second focus detection pixel group are disposed at positions corresponding to pixels sensitive to a color with low luminosity factor in the pixel sets each constituted with a plurality of pixels.
 14. An image sensor according to claim 13, wherein: the pixel sets each include a plurality of pixels sensitive to red, green and blue disposed in a Bayer array, and the first focus detection pixel group and the second focus detection pixel group are disposed at positions corresponding to pixels with sensitivity to blue and green in a two-dimensional array of the imaging pixels.
 15. An image sensor comprising: imaging pixels that convert an image formed via an optical system to image signals; and a first focus detection pixel group and a second focus detection pixel group respectively made up with an array of first focus detection pixels and an array of second focus detection pixels, with the first focus detection pixels and the second focus detection pixels used to receive an image light flux via the optical system to detect a focus adjustment state at the optical system through a pupil division-type method, wherein: an image detection pitch with which the image is detected via the second focus detection pixel group is larger than an image detection pitch with which the image is detected via the first focus detection pixel group; and the first focus detection pixels and the second focus detection pixels each detect a pair of images formed with light fluxes passing through a pair of areas at an exit pupil of the optical system, and an interval between gravitational centers of the pair of areas at the exit pupil of the optical system, which correspond to the second focus detection pixels, is shorter than an interval between gravitational centers of the pair of areas at the exit pupil of the optical system, which corresponds to the first focus detection pixels.
 16. An image sensor comprising: imaging pixels that convert an image formed via an optical system to image signals; and a first focus detection pixel group and a second focus detection pixel group respectively made up with an array of first focus detection pixels and an array of second focus detection pixels, with the first focus detection pixels and the second focus detection pixels used to receive an image light flux via the optical system to detect a focus adjustment state at the optical system through a pupil division-type method, wherein: an image detection pitch with which the image is detected via the second focus detection pixel group is larger than an image detection pitch with which the image is detected via the first focus detection pixel group; and a width over which the pair of areas at the exit pupil of the optical system, which correspond to the second focus detection pixels, range along a direction in which pupils are set side-by-side is smaller than a width over which the pair of areas at the exit pupil of the optical system, which correspond to the first focus detection pixels, range along the direction in which pupils are set side-by-side.
 17. An image sensor comprising: imaging pixels that convert an image formed via an optical system to image signals; and a first focus detection pixel group and a second focus detection pixel group respectively made up with an array of first focus detection pixels and an array of second focus detection pixels, with the first focus detection pixels and the second focus detection pixels used to receive an image light flux via the optical system to detect a focus adjustment state at the optical system through a pupil division-type method, wherein: an image detection pitch with which the image is detected via the second focus detection pixel group is larger than an image detection pitch with which the image is detected via the first focus detection pixel group; and the first focus detection pixels and the second focus detection pixels each include a photoelectric conversion unit disposed at a position further toward one side relative to a pixel center portion.
 18. An imaging device comprising: an image sensor that includes: imaging pixels that convert an image formed via an optical system to image signals and a first focus detection pixel group and a second focus detection pixel group respectively made up with an array of first focus detection pixels and an array of second focus detection pixels, with the first focus detection pixels and the second focus detection pixels used to receive an image light flux via the optical system to detect a focus adjustment state at the optical system through a pupil division-type method; and a focus detection unit that detects the focus adjustment state at the optical system based upon outputs from the first focus detection pixel group and the second focus detection pixel group, wherein: an image detection pitch with which the image is detected via the first focus detection pixel group and an image detection pitch with which the image is detected via the second focus detection pixel group are different from each other.
 19. An imaging device according to claim 18, wherein: the focus detection unit selects one of an output from the first focus detection pixel group and an output from the second focus detection pixel group in correspondence to the focus adjustment state.
 20. An imaging device according to claim 19, further comprising: a pixel output generation unit that generates pixel outputs in correspondence to positions of the first focus detection pixels and the second focus detection pixels based upon outputs from pixels surrounding the first focus detection pixels and the second focus detection pixels.
 21. An image sensor comprising: a first focus detection pixel group made up with an array of first focus detection pixels each equipped with a first photoelectric conversion unit at which an image light flux via an optical system is received so as to detect a focus adjustment state at the optical system through a pupil division-type method based upon an output from the first photoelectric conversion unit; and a second focus detection pixel group made up with an array of second focus detection pixels each equipped with a second photoelectric conversion unit different from the first photoelectric conversion unit so as to detect the focus adjustment state at the optical system through a pupil division-type method based upon an output from the second photoelectric conversion unit.
 22. An image sensor according to claim 21, wherein: an image detection pitch with which the image is detected via the second focus detection pixel group is larger than an image detection pitch at which the image is detected via the first focus detection pixel group.
 23. An image sensor according to claim 22, wherein: an array pitch at which the second focus detection pixels are disposed in the second focus detection pixel group is larger than an array pitch at which the first focus detection pixels are disposed in the first focus detection pixel group.
 24. An imaging method comprising: providing an image sensor that includes imaging pixels that convert an image formed via an optical system to image signals; providing in the image sensor a first focus detection pixel group and a second focus detection pixel group respectively made up with an array of first focus detection pixels and an array of second focus detection pixels, with the first focus detection pixels and the second focus detection pixels used to receive an image light flux via the optical system to detect a focus adjustment state at the optical system through a pupil division-type method; detecting the focus adjustment state at the optical system based upon outputs from the first focus detection pixel group and the second focus detection pixel group; and setting an image detection pitch with which the image is detected via the first focus detection pixel group and an image detection pitch with which the image is detected via the second focus detection pixel group differently from each other.
 25. An imaging method comprising: providing an image sensor that includes an imaging pixel group made up with pixels that convert an image formed via an optical system to image signals, which is formed by arraying a plurality of pixel sets each constituted with a plurality of pixels with sensitivity to different colors; providing in the image sensor a first focus detection pixel group and a second focus detection pixel group respectively made up with an array of first focus detection pixels and an array of second focus detection pixels, with the first focus detection pixels and the second focus detection pixels used to receive an image light flux via the optical system to detect a focus adjustment state at the optical system through a pupil division-type method; detecting the focus adjustment state at the optical system based upon outputs from the first focus detection pixel group and the second focus detection pixel group; and disposing the first focus detection pixel group and the second focus detection pixel group at the image sensor so that an image detection pitch at which the image is detected via the second focus detection pixel group is larger than an image detection pitch at which the image is detected via the first focus detection pixel group, at positions corresponding to pixels sensitive to a color with low luminosity factor in the pixel sets, each constituted with a plurality of pixels.
 26. An imaging method comprising: providing an image sensor that includes imaging pixels that convert an image formed via an optical system to image signals; providing in the image sensor a first focus detection pixel group and a second focus detection pixel group respectively made up with an array of first focus detection pixels and an array of second focus detection pixels, with the first focus detection pixels and the second focus detection pixels used to receive an image light flux via the optical system to detect a focus adjustment state at the optical system through a pupil division-type method; detecting the focus adjustment state at the optical system based upon outputs from the first focus detection pixel group and the second focus detection pixel group, generated by detecting via each of the first focus detection pixels and the second focus detection pixels a pair of images formed with light fluxes passing through a pair of areas at an exit pupil of the optical system; disposing the first focus detection pixel group and the second focus detection pixel group at the image sensor so that an image detection pitch with which the image is detected via the second focus detection pixel group is larger than an image detection pitch with which the image is detected via the first focus detection pixel group; and making an interval between gravitational centers of the pair of areas at the exit pupil of the optical system, which correspond to the second focus detection pixels shorter than an interval between gravitational centers of the pair of areas at the exit pupil of the optical system, which corresponds to the first focus detection pixels.
 27. An imaging method comprising: providing an image sensor that includes imaging pixels that convert an image formed via an optical system to image signals; providing in the image sensor a first focus detection pixel group and a second focus detection pixel group respectively made up with an array of first focus detection pixels and an array of second focus detection pixels, with the first focus detection pixels and the second focus detection pixels used to receive an image light flux via the optical system to detect a focus adjustment state at the optical system through a pupil division-type method; detecting the focus adjustment state at the optical system based upon outputs from the first focus detection pixel group and the second focus detection pixel group; disposing the first focus detection pixel group and the second focus detection pixel group at the image sensor so that an image detection pitch with which the image is detected via the second focus detection pixel group is larger than an image detection pitch with which the image is detected via the first focus detection pixel group; and making a width over which the pair of areas at the exit pupil of the optical system, which correspond to the second focus detection pixels, range along a direction in which pupils are set side-by-side, smaller than a width over which the pair of areas at the exit pupil of the optical system, which correspond to the first focus detection pixels, range along the direction in which the pupils are set side-by-side.
 28. An imaging method comprising: providing an image sensor that includes imaging pixels that convert an image formed via an optical system to image signals; providing in the image sensor a first focus detection pixel group and a second focus detection pixel group respectively made up with an array of first focus detection pixels and an array of second focus detection pixels, with the first focus detection pixels and the second focus detection pixels used to receive an image light flux via the optical system to detect a focus adjustment state at the optical system through a pupil division-type method; detecting a focus adjustment state at the optical system based upon outputs from the first focus detection pixel group and the second focus detection pixel group; disposing the first focus detection pixel group and the second focus detection pixel group at the image sensor so that an image detection pitch with which the image is detected via the second focus detection pixel group is larger than an image detection pitch with which the image is detected via the first focus detection pixel group; and providing a photoelectric conversion unit disposed at a position further toward one side relative to a pixel center portion in the first focus detection pixels and the second focus detection pixels. 